The present invention relates to a process for the production of microporous, permeable, mineral membranes or diaphragms supported by a porous substrate.
More specifically it relates to the production of microporous, permeable, mineral diaphragms or membranes having very small means pore radii, e.g. below 50 .ANG., which can be used for the separation by ultrafiltration of petroleum derivatives e.g. for the regeneration of used or spent oils.
One of the conventional processes for producing microporous membranes consists of depositing on a porous, permeable substrate from a suspension in a liquid of grains or agglomerates of powder grains, one or more active layers, followed by the drying of the deposited layer or layers, the compression thereof and the fritting of the thus obtained assembly, in the manner described in French Pat. No. 2 527 092 filed by the Commissariat a l'Energie Atomique.
According to this prior art process, the compression operation is indispensable thus, said compression is necessary for bringing about a reorganization of the layer or layers deposited on the substrate, so as to obtain a homogeneous, microporous texture and for obtaining a good mechanical strength by increasing the cohesion within the layer or layers and possibly there adhesion to the substrate. Moreover, with this prior art process, it is necessary to start with a suspension of powders in a liquid, so that it is difficult to obtain membranes with pores of very small sizes.